In-situ pad and wafer cleaning during chemical mechanical polishing

ABSTRACT

A method for in-situ cleaning a polishing pad and a wafer surface simultaneously during copper chemical mechanical polishing and an apparatus for carrying out such method are disclosed. The method is carried out by dispensing an acid-containing solution onto a top surface of a polishing pad while the wafer is rotated against the polishing pad without any slurry solution being dispensed. The acid-containing solution may be advantageously formed by diluting an acid such as citric acid, HCOOH, CH 3 COOH, HNO 3 , H 2 SO 4  and HF to a concentration of less than 10 wt. % acid, preferably less than 5 wt. % acid, and more preferably less than 1 wt. % acid. The acid-containing solution may be dispensed onto a top surface of the polishing pad for a time period between about 30 sec. and about 300 sec.

FIELD OF THE INVENTION

[0001] The present invention generally relates to a chemical mechanical polishing method for metal conductors on a semiconductor wafer and more particularly, relates to a method and apparatus for in-situ cleaning a pad and a wafer during chemical mechanical polishing copper conductors on a semiconductor wafer by using an acid-containing cleaning solution.

BACKGROUND OF THE INVENTION

[0002] Apparatus for polishing thin, flat semi-conductor wafers is well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.

[0003] More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.

[0004] A perspective view of a typical CMP apparatus is shown in FIG. 1A. The CMP apparatus 10 consists of a controlled mini-environment 12 and a control panel section 14. In the controlled mini-environment 12, typically four spindles 16, 18, 20, and 22 are provided (the fourth spindle 22 is not shown in FIG. 1A) which are mounted on a cross-head 24. On the bottom of each spindle, for instance, under the spindle 16, a polishing head 26 is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head 26 with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head 26 is moved longitudinally along the spindle 16 in a linear motion across the surface of a polishing pad 28. As shown in FIG. 1A, the polishing pad 28 is mounted on a polishing disc 30 rotated by a motor (not shown) in a direction opposite to the rotational direction of the polishing head 26.

[0005] Also shown in FIG. 1A is a conditioner arm 32 which is equipped with a rotating conditioner disc 34. The conditioner arm 32 pivots on its base 36 for conditioning the polishing pad 38 for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad 28, 38 and 40 are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head 24 rotates 90° clockwise to move the wafer just loaded into a polishing position, i.e., over the polishing pad 28. Simultaneously, a polished wafer mounted on spindle 20 is moved into the head clean load/unload station for unloading.

[0006] A cross-sectional view of a polishing station 42 is shown in FIGS. 1B and 1C. As shown in FIG. 1B, a rotating polishing head 26 which holds a wafer 44 is pressed onto an oppositely rotating polishing pad 28 mounted on a polishing disc 30 by adhesive means. The polishing pad 28 is pressed against the wafer surface 46 at a predetermined pressure. During polishing, a slurry 48 is dispensed in droplets onto the surface of the polishing pad 28 to effectuate the chemical mechanical removal of materials from the wafer surface 46.

[0007] An enlarged cross-sectional representation of the polishing action which results form a combination of chemical and mechanical effects is shown in FIG. 1C. The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.

[0008] During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a pH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e, hard particles and components that chemically react with the surface of the substrate.

[0009] For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e, larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina (Al₃O₂)may also be used in the slurry composition.

[0010] The polishing pad 28 is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about 12 hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.

[0011] Referring now to FIG. 2, wherein a perspective view of a CMP polishing station 42 is shown. The polishing station 42 consists of a conditioning head 52, a polishing pad 28, and a slurry delivery arm 54 positioned over the polishing pad. The conditioning head 28 is mounted on a conditioning arm 58 which is extended over the top of the polishing pad 28 for making sweeping motion across the entire surface of the pad. The slurry delivery arm 54 is equipped with a single slurry dispensing nozzle 62 which is used for dispensing a slurry solution on the top surface 60 of the polishing pad 56. Surface grooves 64 are further provided in the top surface 60 to facilitate even distribution of the slurry solution and to help entrapping undesirable particles that are generated by coagulated slurry solution or any other foreign particles which have fallen on top of the polishing pad during a polishing process. The surface grooves 64 while serving an important function of distributing the slurry also presents a processing problem when the pad surface 60 gradually worn out after successive use.

[0012] A problem frequently encountered in using polishing pads in a CMP process for oxide planarization is the rapid deterioration in polishing rates of the oxide with successive wafers. The cause for the deterioration has been shown to be due to an effect known as “pad glazing” wherein the surface of the polishing pads become smooth such that the pads can no longer hold slurry in-between the fibers. This has been found to be a physical phenomenon on the surface, and is not caused by any chemical reactions between the pad and the slurry.

[0013] To remedy the pad glazing effect, numerous techniques of pad conditioning or scrubbing have been proposed to regenerate and restore the pad surface and thereby, restoring the polishing rates of the pad. The pad conditioning techniques include the use of silicon carbide particles, diamond emery paper, blade or knife for scrapping the polishing pad surface. The goal of the conditioning process is to remove polishing debris from the pad surface, reopen the pores, and thus forms micro scratches in the surface of the pad for improved life time of the pad surface. The pad conditioning process can be carried out either during a polishing process, i.e., known as concurrent conditioning, or after a polishing process.

[0014] Another processing difficulty frequently incurred in utilizing the pad conditioning disc is that while the conditioning disc may be effective in alleviating the pad glazing problem, it may not be effective in physically removing particles from the polishing pad surface, specifically, when the particles are trapped in the surface grooves. The source of the particles may be the diamond particles that have dislodged from the conditioning pad surface, coagulated or dried-up particles from the slurry solution or any other contaminating particles such as polishing debris that may have fallen onto the polishing pad surface. The particle contamination problem becomes more serious with the continuous usage of the polishing pad since as the pad surface is gradually warned out, the depth of the grooves in the pad surface becomes smaller and thus no longer able to hold the particles therein. When the particles are released from the grooves onto the top of the polishing pad, severe scratching or other equally harmful damages to the wafer surface can occur.

[0015]FIGS. 3A and 3B are graphs illustrating the particle contamination problem on a polishing pad which is conditioned by a conventional conditioning head. For instance, FIG. 3A illustrates that at or near a pad life of 10˜12.5 hours, the particle contamination problem becomes much more serious in that the failure rate doubles and quintuples those rates obtained at below the 10 hour pad life. This is a clear indication that, after 10 hours use of the polishing pad, the grooves become substantially shallower and are no longer capable of holding the contaminating particles therein. After a pad usage of more than 12.5 hours, the failure rate in wafer lots polished exceeds 50% which is clearly unacceptable. Similar trend is also seen in FIG. 3B which illustrate the dependency of particle counts on the pad life. It shows that after a pad life of 10 hours, there is a significant increase (at a faster rate) in the particle counts.

[0016] The particle contamination problem on a polishing pad surface is therefore a serious processing problem that must be resolved in order for the chemical mechanical polishing process to be used as a reliable planarization technique. In an attempt to solve the particle problem, efforts have been made to flush a polishing pad surface with high pressure deionized water jet to remove particles entrapped in the surface grooves. Other efforts have been made to manually clean the polishing pad by brushing after shutting down the chemical mechanical polishing apparatus. Neither method produces satisfactory results in obtaining a polishing pad surface that is substantially without particles. Moreover, the method either requires the complete shut-down of the polishing apparatus and thus a reduction in the fabrication yield, or requires an interruption of the polishing process in order to flush the pad with deionized water.

[0017] In chemical mechanical polishing copper conductors on a semiconductor wafer, processing difficulties occur due to the formation of various compounds of copper oxide, i.e., cupric oxide (CuO) and cuprous oxide (Cu₂O). The CMP byproducts of Cu_(x)O are frequently embedded in the pad grooves and may cause damages or scratches to the surface of a wafer during the polishing process. Furthermore, with the pad grooves filled with the polishing byproducts, the removal rate is reduced resulting in a reduction in the fabrication yield. The copper polishing byproducts of Cu_(x)O must therefore be removed after the completion of a CMP process.

[0018] It is therefore an object of the present invention to provide a method for cleaning a polishing pad and a wafer surface after a copper CMP process that does not have the drawbacks or shortcomings of the conventional methods.

[0019] It is another object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface during a copper chemical mechanical polishing process by removing polishing byproducts of Cu_(x)O.

[0020] It is a further object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface during a copper CMP process by using an acid-containing cleaning solution.

[0021] It is another further object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface simultaneously during a copper CMP process by dispensing an acid-containing cleaning solution onto a top surface of the polishing pad while the wafer and the pad are being rotated.

[0022] It is still another object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface simultaneously during a copper CMP process by dispensing an acid-containing cleaning solution that contains HCOOH, CH₃COOH, HNO₃, H₂SO₄ or HF.

[0023] It is yet another object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface simultaneously during a copper CMP process by dispensing an acid-containing cleaning solution which contains less than 1 wt. % acid onto the surface of the polishing pad.

[0024] It is still another further object of the present invention to provide a chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head for dispensing an acid-containing solution onto a top surface of the polishing pad.

[0025] It is yet another further object of the present invention to provide a method for in-situ cleaning a polishing pad and a wafer surface during a copper chemical mechanical polishing process by removing polishing byproducts of Cu_(x)O.

[0026] It is still another further object of the present invention to provide a chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head equipped with a plurality of dispensing nozzles for dispensing an acid-containing solution over the entire surface area of the polishing pad.

SUMMARY OF THE INVENTION

[0027] In accordance with the present invention, a method for in-situ cleaning a polishing pad and a wafer surface simultaneously during a copper chemical mechanical polishing process and an apparatus for conducting such method are disclosed.

[0028] In a preferred embodiment, a method for in-situ cleaning a polishing pad and a wafer surface during copper CMP can be carried out by rotating a wafer and a polishing pad in opposite directions; conducting a chemical mechanical polishing process on a wafer surface; stopping the dispensing of a slurry solution onto a top surface of the polishing pad; and dispensing an acid-containing solution onto the top surface of the polishing pad while the wafer and the pad are being rotated.

[0029] The method for in-situ cleaning a pad and a wafer surface during copper CMP may further include the step of mixing the acid-containing solution from water and an acid selected from the group consisting of citric acid, HCOOH, CH₃COOH, HNO₃, H₂SO₄ and HF. The method may further include the step of mixing the acid-containing solution to a concentration of not higher than 10 wt. % acid. The method may further include the step of dispensing the acid-containing solution for a time period of at least 30 sec., or the step of dispensing the acid-containing solution for a time period of between about 30 sec. and about 300 sec. The method may further include the step of dispensing the acid-containing solution in a concentration of not higher than 5 wt. % acid, or preferably not higher than 1 wt. % acid. The method may further include the step of mixing the acid-containing solution in 0.5 wt. % citric acid and 99.5 wt. % water. The method may further include the step of removing Cu_(x)O from the pad and the wafer by the acid-containing solution. The method may further include the step of dispensing the acid-containing solution while the wafer and the pad are rotated in opposite directions at a rotational speed of at least 50 rpm.

[0030] The present invention is further directed to a chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head which includes a wafer carrier for holding a wafer therein and for rotating the wafer at a first rotational direction; a polishing platen for holding a polishing pad thereon and for rotating the pad at a second rotational direction opposite to the first rotational direction; a slurry dispensing arm for dispensing a slurry solution from a dispensing nozzle onto a top surface of the polishing pad; and a cleaning solution dispensing arm for dispensing an acid-containing solution from a dispensing nozzle onto the top surface of the polishing pad.

[0031] The chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head may further include metering means for metering components for the acid-containing solution. The cleaning solution dispensing arm may further include at least one dispensing nozzle for dispensing the acid-containing solution, of a plurality of dispensing nozzles for dispensing the acid-containing solution substantially over the entire surface of the polishing pad. Apparatus may further include mixing means for mixing the components that are metered by the metering means for making the acid-containing solution. The apparatus may further include the pad conditioning arm and a pad conditioning disk for conditioning the polishing pad. The cleaning solution dispensing arm may be connected unitarily to the slurry dispensing arm for dispensing the acid-containing solution. The apparatus may further include an interlock means for dispensing the acid-containing solution only when the dispensing of the slurry solution is stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:

[0033]FIG. 1A is a perspective view of a conventional chemical mechanical polishing apparatus incorporating three polishing stations.

[0034]FIG. 1B is a cross-sectional view of a wafer carrier and a polishing pad engaging a wafer mounted in the carrier.

[0035]FIG. 1C is an enlarged, cross-sectional view illustrating a slurry interaction between a wafer surface and a polishing pad surface.

[0036]FIG. 2 is a perspective view of a polishing station in a CMP apparatus equipped with a slurry dispensing arm and a pad conditioning arm.

[0037]FIG. 3A is a graph illustrating the dependency of failure rates on polished pad life in a conventional CMP apparatus.

[0038]FIG. 3B is a graph illustrating the dependency of particle counts on pad life in a conventional CMP apparatus.

[0039]FIG. 4 is a perspective view of the present invention CMP apparatus incorporating a cleaning solution dispensing arm.

[0040]FIG. 5 is block diagram illustrating the present invention cleaning solution dispensing system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The present invention discloses a method for in-situ cleaning a polishing pad and a wafer surface simultaneously during a copper CMP process. The invention further discloses a chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head for the simultaneous cleaning of the pad and the wafer during the CMP process.

[0042] The method for in-situ cleaning a pad and a wafer simultaneously during a copper CMP process can be carried out by first rotating a wafer and a polishing pad in opposite directions; then conducting a chemical mechanical polishing process on a wafer surface; stopping the dispensing of a slurry solution onto a top surface of the polishing pad; and dispensing an acid-containing solution onto the top surface of the polishing pad while the wafer and the pad are being rotated.

[0043] A suitable acid for use in the present invention acid-containing solution may be selected from citric acid, HCOOH, CH₃COOH, HNO₃, H₂SO₄ and HF. The acid-containing solution is mixed by the acid and a diluting liquid such as water to a concentration of not higher than 10 wt. % acid, preferably to not higher than 5 wt. % acid, and more preferably to not higher than 1 wt. % acid. The method can be carried out by dispensing the acid-containing solution onto a top surface of a polishing pad for a time period of at least 30 sec., or for a time period of between about 30 sec. and about 300 sec.

[0044] In a preferred embodiment, the acid-containing solution is mixed by 0.4 wt. % citric acid and 99.5 wt. % water.

[0045] The invention further discloses a chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head which includes a wafer carrier, a polishing platen, a slurry dispensing arm and a cleaning solution dispensing arm. The wafer carrier is adapted for holding a wafer therein and for rotating the wafer in a first rotational direction. The polishing platen is adapted for holding a polishing pad and for rotating the pad in a second rotational direction that is opposite to the first rotational direction of the wafer carrier. The slurry dispensing arm is adapted for dispensing a slurry solution from a dispensing nozzle onto a top surface of the polishing pad, while the cleaning solution dispensing arm is adapted for dispensing an acid-containing solution from a dispensing nozzle onto the top surface of the polishing pad. The apparatus may further include means for metering and mixing the components for the acid-containing solution. The cleaning solution dispensing arm may include at least one dispensing nozzle, and preferably a plurality of dispensing nozzles for dispensing the acid-containing solution over the entire surface of a polishing pad. The cleaning solution dispensing arm may be unitarily formed with the slurry dispensing arm for dispensing an acid-containing solution. The apparatus may further include an interlocking means for dispensing the acid-containing solution only when the dispensing of the slurry solution is stopped.

[0046] The novel method provided by the invention effectively removes Cu_(x)O of either cupric oxide or cuprous oxide from a wafer surface and a polishing pad during a copper CMP process by dispensing a diluted acid solution onto the pad and the wafer. The acid-containing solution is dispensed while the polishing pad and the wafer are rotated at opposite directions by incorporating the acid cleaning step as part of the polishing recipe. By removing the embedded Cu_(x)O from the polishing pad, the copper CMP process defects can be reduced while the CMP removal rate can be maintained and stabilized. Furthermore, copper morphology is also improved after a CMP process. The present invention utilizes, instead of a standard pad cleaning by DI water or by a slurry, an in-situ pad and wafer cleaning by diluted citric acid to simultaneously remove embedded byproducts of copper CMP from the pad surface and the wafer surface and thus, achieving improved morphology on the copper surface.

[0047] The present invention novel method of dispensing acid-containing solution for cleaning the Cu_(x)O from the polishing pad and wafer surfaces is carried out while the wafer is still rotating on the polishing pad. However, the dispensing of polishing slurry is stopped during the acid solution cleaning step.

[0048] Referring now to FIG. 4, wherein a present invention polishing station 70 is shown. Polishing station 70, while similar in other aspects to the conventional polishing station 42 shown in FIG. 2, is further equipped with an acid-containing cleaning solution dispensing arm 74. The acid-containing cleaning solution dispensing arm 74 dispenses the acid-containing solution through dispensing nozzle 78 positioned at the tip portion 82 of the dispensing arm 74. The operation of the acid-containing cleaning solution dispensing arm 74 is further illustrated in FIG. 5 in a block diagram.

[0049] The cleaning solution supply 86 consists of a metering portion 88 and a mixing portion 90. In the metering portion 88, chemical components A and B are first fed into a metering portion for measuring an accurate amount of the component for feeding into the mixing portion 90. For instance, the component A may be a 40% citric acid, while the component B may be DI water. The precise amounts of the components A and B, which are determined and measured by a process controller (not shown) are then mixed in the mixing portion 90 before it is dispensed onto a top surface of a polishing pad 92. Onto the top of the polishing pad, is further provided a slurry supply system 94 for feeding a slurry supply onto the polishing pad 92. In between the slurry supply system 94 and the cleaning solution supply system 86, is further provided an interlocking means 96 which is capable of preventing the dispensing of any cleaning solution while the slurry solution is being dispensed onto the polishing pad 92. The cleaning solution is therefore dispensed onto the polishing pad only when the dispensing of the slurry solution has stopped. This assures a thorough and effective cleaning of the polishing pad and the wafer surface after a copper CMP process, as part of the copper CMP process.

[0050] Various diluted acid solutions may be utilized in the present invention novel cleaning method. For instance, these acids include citric acid, HCOOH, CH₃COOH, HNO₃, H₂SO₄ and HF. A large dilution ratio is preferred for the acid-containing solution, for instance, a concentration of not higher than 10 wt. % acid, preferably not higher than 5 wt. % acid, and more preferably not higher than 1 wt. % acid. In a preferred embodiment, when a diluted citric acid is utilized, the acid-containing solution contains 0.4 wt. % citric acid in DI water.

[0051] A suitable time period for dispensing the acid-containing solution onto a polishing pad surface is at least 30 sec., and preferably for a time period between about 30 sec. and about 300 sec. The present invention novel method effectively removes Cu_(x)O from the surface of a polishing pad and the surface of a wafer by an acid-containing solution, such as the 0.4 wt. % citric acid solution. The cleaning step should be carried out by dispensing the acid-containing solution onto the polishing pad surface while the wafer and the pad are rotated in opposite directions against each other at a rotational speed of at least 50 rpm, and preferably at least 100 rpm.

[0052] The invention further provides a chemical mechanical polishing apparatus that incorporates an in-situ pad and wafer cleaning head that includes a wafer carrier, a polishing platen and a polishing pad adhesively joined to the platen, a slurry dispensing arm, and a cleaning solution dispensing arm. The apparatus may further include a metering means and a mixing means for metering and mixing components for the acid-containing solution, i.e., in the preferred embodiment, the components of citric acid and DI water. The apparatus further includes at least one dispensing nozzle, and preferably a plurality of dispensing nozzles for dispensing the acid-containing solution onto a top surface of a polishing pad. When a plurality of dispensing nozzles is used, the entire surface area of the polishing pad can be covered by the dispensing nozzles. The apparatus may further be provided with a cleaning solution dispensing arm that may be unitarily connected to a slurry dispensing arm for dispensing the acid-containing solution. The apparatus may still further include an interlocking means for allowing the dispensing of the acid-containing solution only when the dispensing of the slurry solution is stopped.

[0053] The present invention novel method for in-situ cleaning a polishing pad and a wafer surface during a copper CMP process and an apparatus for carrying out such cleaning have therefore been amply described in the above description and in the appended drawings of FIGS. 4 and 5.

[0054] While the present invention has been described in an illustrative manner, it should be understood that the terminology used is intended to be in a nature of words of description rather than of limitation.

[0055] Furthermore, while the present invention has been described in terms of a preferred embodiment, it is to be appreciated that those skilled in the art will readily apply these teachings to other possible variations of the inventions.

[0056] The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows. 

What is claimed is:
 1. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing comprising the steps of: rotating a wafer and a polishing pad in opposite directions; conducting a chemical mechanical polishing process on a wafer surface; stopping the dispensing of a slurry solution onto a top surface of said polishing pad; and dispensing an acid-containing solution onto said top surface of said polishing pad while said wafer and said pad are being rotated.
 2. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of mixing said acid-containing solution from water and an acid selected from the group consisting of citric acid, HCOOH, CH₃COOH, HNO₃, H₂SO₄ and HF.
 3. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of mixing said acid-containing solution to a concentration of not higher than 10 wt. % acid.
 4. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of dispensing said acid-containing solution for a time period of at least 30 sec.
 5. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of dispensing said acid-containing solution for a time period of between about 30 sec. and about 300 sec.
 6. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of dispensing said acid-containing solution to a concentration of preferably not higher than 5 wt. % acid.
 7. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of dispensing said acid-containing solution to a concentration of more preferably not higher than 1 wt. % acid.
 8. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of mixing said acid-containing solution by 0.4 wt. % citric acid and 99.5 wt. % water.
 9. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of removing Cu_(x)O from said pad and said wafer by said acid-containing solution.
 10. A method for in-situ cleaning a pad and a wafer during chemical mechanical polishing according to claim 1 further comprising the step of dispensing said acid-containing solution while said wafer and said pad are rotated in opposite directions at a rotational speed of at least 50 rpm.
 11. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head comprising: a wafer carrier for holding a wafer therein and for rotating the wafer at a first rotational direction; a polishing platen for holding a polishing pad thereon and for rotating the pad at a second rotational direction opposite to said first rotational direction; a slurry dispensing arm for dispensing a slurry solution from a dispensing nozzle onto a top surface of the polishing pad; and a cleaning solution dispensing arm for dispensing an acid-containing solution from a dispensing nozzle onto said top surface of the polishing pad.
 12. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11 further comprising metering means for metering components for said acid-containing solution.
 13. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11, wherein said cleaning solution dispensing arm further comprises at least one dispensing nozzle for dispensing said acid-containing solution.
 14. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11, wherein said cleaning solution dispensing arm further comprises a plurality of dispensing nozzles for dispensing said acid-containing solution substantially over the entire surface of said polishing pad.
 15. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 12 further comprising mixing means for mixing said components that are metered by said metering means for making said acid-containing solution.
 16. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11 further comprising a pad conditioning arm and a pad conditioning disk for conditioning said polishing pad.
 17. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11, wherein said cleaning solution dispensing arm being connected unitarily to said slurry dispensing arm for dispensing said acid-containing solution.
 18. A chemical mechanical polishing apparatus incorporating an in-situ pad and wafer cleaning head according to claim 11 further comprising an interlock means for dispensing said acid-containing solution only when said dispensing of the slurry solution is stopped. 